A laser printer is known in which a semiconductor laser is driven by a modulated signal obtained by modulating an image signal and an electrostatic latent image is formed on a photoconductive drum by a laser beam emitted from the semiconductor laser, so that an image is formed. During printing, if the printer is vibrated, a scanning line of the laser beam is shifted (displaced) in the sub-scanning direction due to the vibration of the optical system or the tilt of the polygon caused by the shock of the vibration. The displacement of the scanning line has resulted in pitch unevenness, and has caused the deterioration in the quality of a printed image. In order to soften the shock and vibration to the optical system including the laser and the mirror and the like, a proposal has been made in which, the optical system is mounted in the main body of the printer via a shock absorber, the enhancement of printing efficiency is achieved (refer to Japanese Laid-Open No. 09-146324).
In order to suppress the pitch unevenness, a damper has been provided on an easy-to-vibrate portion of a printer so that vibration within the printer is not transferred to the optical system, and a method has been employed in which the rigidity of the optical system is enhanced, by employing aluminum die-casting. With regard to the tilt of the polygon, there has been no other method than reducing the profile irregularity, and the foregoing methods for the pitch unevenness and the tilt of the polygon have been significantly costly.